Numerical ordering and symbolic arithmetic share frontal and parietal circuits in the right hemisphere.

A prominent proposal in numerical cognition states that our mental calculation abilities are grounded in the approximate number system (ANS). Recently, it was proposed that this association is mediated by numerical ordering abilities. As a first step in elucidating the neural correlates of this link this study tested which areas in the human brain carry information common to both calculation and numerical ordering. While lying in an MR scanner 17 healthy participants (a) decided whether or not a given number triplet was presented in numerically ascending order, and (b) solved simple addition and subtraction problems. Standard general linear model analyses revealed a largely overlapping network in fronto-parietal regions for both tasks. By analyzing the spatial information over voxels using a whole-brain searchlight algorithm we identified a right hemispheric network comprising areas along the intraparietal sulcus and in the inferior frontal cortex which was similarly involved in order judgments and symbolic arithmetic. Functional and anatomical characteristics of this network make it a candidate for linking the ANS to mental arithmetic.